1. Field of the Disclosure
Embodiments of the present disclosure relate to a sift-by-wire fail control device for a vehicle with an automatic transmission (e.g., a continuously variable or “stepless” transmission, a step automatic transmission, or an automated manual transmission capable of automatically shifting gears of a manual transmission).
2. Description of the Related Art
An typical automatic transmission has a park (P) range, a reverse travel (R) range, a neutral (N) range, a forward automatic transmission (D) range, and the like, determining respective gear-shift modes, in that order. A driver may perform a manual selection operation among these ranges. A manual valve is moved in accordance with the selection operation. When the manual valve is located at a position corresponding to the selected range, gear-shift corresponding to the selected range is obtained.
Thus, a shift lever operated by a driver has been typically mechanically coupled with a manual valve by a link mechanism, a wire, or the like, and hence, the manual valve has been moved in accordance with a selection operation using the mechanical system.
Because the link mechanism, the wire, or the like, is provided, the mechanical system may require a relatively large amount of (volumetric) space. In addition, the use of electronic control and the reduction in size of vehicles are becoming more commonplace in recent years. Thus, a so-called “shift-by-wire” automatic transmission has been suggested, in which a manual valve is moved in accordance with a selection operation by a driver under electronic control.
In the former shift-by-wire system, the selection operation with the shift lever is electronically detected, an actuator is moved in accordance with a detection signal, and the manual valve is shifted to a range position corresponding to the selection operation.
The system meets the requirements for electronic control reduction in size of vehicles because the large arrangement space for the mechanical system, such as the link mechanism or the wire, is not necessary.
In the shift-by-wire system, because the manual valve is moved in accordance with the selection operation under the electronic control, it is important to take a measure for fail-safe, to prepare for an unexpected situation, such as that the manual valve is not moved in accordance with the selection operation due to a failure in the actuator or a failure in an electronic control system.
Formerly, for example, Japanese Unexamined Patent Application Publication No. 06-213025 suggested a mechanism for fail-safe. In the mechanism, the output of an engine was reduced when a failure occurs in a traveling condition, the failure in which a manual valve is not moved in accordance with a selection operation; and the operation of the engine was stopped when the failure occurs in a stop condition.
Unfortunately, with such a mechanism for fail-safe, the operation of the engine is unconditionally stopped in any situation when a vehicle is stopped and if the failure, in which the manual valve is not moved in accordance with the selection operation, occurs. Hence, the vehicle is inhibited from traveling.
Therefore, even when a driver intends to drive the vehicle to a repair shop, to the driver's home, or to a safe parking location, the vehicle may not travel from a stopped position under its own power, and hence, the vehicle must be moved by a wrecker or tow truck.